The present invention relates to a heat exchanger in a simple structure which can be applied to a heat exchanger (EGR cooler) used in an exhaust gas recirculation apparatus in an automobile and other heat exchangers, in which a core body formed by bending a strip-shaped metal plate in a fanfold manner, and having flat first flow passages and second flow passages alternately in the thickness direction of the metal plate, each of the first flow passages of the core body being blocked by each tooth of a pair of comb-state members at both end positions.
A conventional EGR cooler is made of an assembly of a large number of flat tubes or a large number of plates, a large number of fins, a casing and a header, in which cooling water is made to communicate through the casing side and an exhaust gas is made to communicate inside each of the flat tubes or the like as proposed in the invention described in Japanese Patent Application Laid-Open No. 5-18634.
Another heat exchanger is proposed in which a core of the heat exchanger is formed by a strip-shaped metal plate bent in a fanfold manner and a pair of comb-state members, the outer periphery being fitted with a cylindrical casing, and tanks are provided at both ends thereof in the longitudinal direction and as in the invention described in WO 2004/065876 A1.
In the former heat exchanger such as the EGR cooler, the number of parts is large, which makes assembling cumbersome and increases the number of brazing portions on the parts, and there is a problem that a leakage tends to occur at the brazing portion.
In the latter heat exchanger, the core body is formed in a shape of turning-up in a fanfold state to create a plurality of flat groove portions, while providing the first flow passage and the second flow passage alternately, the first flow passage being provided with a comb tooth of a comb-state member, thus joining the groove bottom with the front end of the comb tooth. And the casing is fitted with the outer periphery of the core body. The casing is made of a channel-state member covering the three sides of outer periphery of the core body and a lid member to close the opening of the channel-state member, being formed into a cylindrical shape, while both ends thereof are connected to headers. A pair of cooling water tanks are located at both end portions of the lid member, thus the cooling water communicates into the respective first flow passages of the core body through the inlet/outlet pipes attached to both ends of the lid member. The exhaust gas communicates through the second flow passage, thus the heat exchange is conducted between the exhaust gas and the cooling water.
According to an experiment of the inventors of the present invention, however, in the latter heat exchanger, when the inlet/outlet pipes and one of the inlet/outlet ports of the first flow passage face with each other, the first fluid flowing in and out from the inlet/outlet pipes tends to flow in an excessive amount at the inlet/outlet pipe side during flowing through individual first flow passages. The phenomenon leads to non-uniform flow of the first fluid in individual flow passages, which induces remaining of the first fluid at a portion of the flow passage. Thus, the heat exchange at the stagnant fluid portion decreases to generate overheating portion, which is a defective phenomenon.
To this point, the present invention aims to solve the above problems.